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/** @license
* DHTML Snowstorm! JavaScript-based Snow for web pages
* --------------------------------------------------------
* Version 1.41.20101113 (Previous rev: 1.4.20091115)
* Copyright (c) 2007, Scott Schiller. All rights reserved.
* Code provided under the BSD License:
* http://schillmania.com/projects/snowstorm/license.txt
*/

/*global window, document, navigator, clearInterval, setInterval */
/*jslint white: false, onevar: true, plusplus: false, undef: true, nomen: true, eqeqeq: true, bitwise: true, regexp: true, newcap: true, immed: true */

var snowStorm = (function(window, document) {

// --- common properties ---

this.flakesMax = 128; // Limit total amount of snow made (falling + sticking)
this.flakesMaxActive = 64; // Limit amount of snow falling at once (less = lower CPU use)
this.animationInterval = 33; // Theoretical "miliseconds per frame" measurement. 20 = fast + smooth, but high CPU use. 50 = more conservative, but slower
this.excludeMobile = true; // Snow is likely to be bad news for mobile phones' CPUs (and batteries.) By default, be nice.
this.flakeBottom = null; // Integer for Y axis snow limit, 0 or null for "full-screen" snow effect
this.followMouse = true; // Snow movement can respond to the user's mouse
this.snowColor = '#fff'; // Don't eat (or use?) yellow snow.
this.snowCharacter = '•'; // • = bullet, · is square on some systems etc.
this.snowStick = true; // Whether or not snow should "stick" at the bottom. When off, will never collect.
this.targetElement = null; // element which snow will be appended to (null = document.body) - can be an element ID eg. 'myDiv', or a DOM node reference
this.useMeltEffect = true; // When recycling fallen snow (or rarely, when falling), have it "melt" and fade out if browser supports it
this.useTwinkleEffect = false; // Allow snow to randomly "flicker" in and out of view while falling
this.usePositionFixed = false; // true = snow does not shift vertically when scrolling. May increase CPU load, disabled by default - if enabled, used only where supported

// --- less-used bits ---

this.freezeOnBlur = true; // Only snow when the window is in focus (foreground.) Saves CPU.
this.flakeLeftOffset = 0; // Left margin/gutter space on edge of container (eg. browser window.) Bump up these values if seeing horizontal scrollbars.
this.flakeRightOffset = 0; // Right margin/gutter space on edge of container
this.flakeWidth = 8; // Max pixel width reserved for snow element
this.flakeHeight = 8; // Max pixel height reserved for snow element
this.vMaxX = 5; // Maximum X velocity range for snow
this.vMaxY = 4; // Maximum Y velocity range for snow
this.zIndex = 0; // CSS stacking order applied to each snowflake

// --- End of user section ---

var s = this, storm = this, i,
// UA sniffing and backCompat rendering mode checks for fixed position, etc.
isIE = navigator.userAgent.match(/msie/i),
isIE6 = navigator.userAgent.match(/msie 6/i),
isWin98 = navigator.appVersion.match(/windows 98/i),
isMobile = navigator.userAgent.match(/mobile/i),
isBackCompatIE = (isIE && document.compatMode === 'BackCompat'),
noFixed = (isMobile || isBackCompatIE || isIE6),
screenX = null, screenX2 = null, screenY = null, scrollY = null, vRndX = null, vRndY = null,
windOffset = 1,
windMultiplier = 2,
flakeTypes = 6,
fixedForEverything = false,
opacitySupported = (function(){
try {
document.createElement('div').style.opacity = '0.5';
} catch(e) {
return false;
}
return true;
}()),
didInit = false,
docFrag = document.createDocumentFragment();

this.timers = [];
this.flakes = [];
this.disabled = false;
this.active = false;
this.meltFrameCount = 20;
this.meltFrames = [];

this.events = (function() {

var old = (window.attachEvent), slice = Array.prototype.slice,
evt = {
add: (old?'attachEvent':'addEventListener'),
remove: (old?'detachEvent':'removeEventListener')
};

function getArgs(oArgs) {
var args = slice.call(oArgs), len = args.length;
if (old) {
args[1] = 'on' + args[1]; // prefix
if (len > 3) {
args.pop(); // no capture
}
} else if (len === 3) {
args.push(false);
}
return args;
}

function apply(args, sType) {
var oFunc = args.shift()[evt[sType]];
if (old) {
oFunc(args[0], args[1]);
} else {
oFunc.apply(this, args);
}
}

function addEvent() {
apply(getArgs(arguments), 'add');
}

function removeEvent() {
apply(getArgs(arguments), 'remove');
}

return {
add: addEvent,
remove: removeEvent
};

}());

function rnd(n,min) {
if (isNaN(min)) {
min = 0;
}
return (Math.random()*n)+min;
}

function plusMinus(n) {
return (parseInt(rnd(2),10)===1?n*-1:n);
}

this.randomizeWind = function() {
vRndX = plusMinus(rnd(s.vMaxX,0.2));
vRndY = rnd(s.vMaxY,0.2);
if (this.flakes) {
for (var i=0; i<this.flakes.length; i++) {
if (this.flakes[i].active) {
this.flakes[i].setVelocities();
}
}
}
};

this.scrollHandler = function() {
// "attach" snowflakes to bottom of window if no absolute bottom value was given
scrollY = (s.flakeBottom?0:parseInt(window.scrollY||document.documentElement.scrollTop||document.body.scrollTop,10));
if (isNaN(scrollY)) {
scrollY = 0; // Netscape 6 scroll fix
}
if (!fixedForEverything && !s.flakeBottom && s.flakes) {
for (var i=s.flakes.length; i-- {
if (s.flakes[i].active === 0) {
s.flakes[i].stick();
}
}
}
};

this.resizeHandler = function() {
if (window.innerWidth || window.innerHeight) {
screenX = window.innerWidth-(!isIE?16:2)-s.flakeRightOffset;
screenY = (s.flakeBottom?s.flakeBottom:window.innerHeight);
} else {
screenX = (document.documentElement.clientWidth||document.body.clientWidth||document.body.scrollWidth)-(!isIE?8:0)-s.flakeRightOffset;
screenY = s.flakeBottom?s.flakeBottom:(document.documentElement.clientHeight||document.body.clientHeight||document.body.scrollHeight);
}
screenX2 = parseInt(screenX/2,10);
};

this.resizeHandlerAlt = function() {
screenX = s.targetElement.offsetLeft+s.targetElement.offsetWidth-s.flakeRightOffset;
screenY = s.flakeBottom?s.flakeBottom:s.targetElement.offsetTop+s.targetElement.offsetHeight;
screenX2 = parseInt(screenX/2,10);
};

this.freeze = function() {
// pause animation
if (!s.disabled) {
s.disabled = 1;
} else {
return false;
}
for (var i=s.timers.length; i-- {
clearInterval(s.timers[i]);
}
};

this.resume = function() {
if (s.disabled) {
s.disabled = 0;
} else {
return false;
}
s.timerInit();
};

this.toggleSnow = function() {
if (!s.flakes.length) {
// first run
s.start();
} else {
s.active = !s.active;
if (s.active) {
s.show();
s.resume();
} else {
s.stop();
s.freeze();
}
}
};

this.stop = function() {
this.freeze();
for (var i=this.flakes.length; i-- {
this.flakes[i].o.style.display = 'none';
}
s.events.remove(window,'scroll',s.scrollHandler);
s.events.remove(window,'resize',s.resizeHandler);
if (s.freezeOnBlur) {
if (isIE) {
s.events.remove(document,'focusout',s.freeze);
s.events.remove(document,'focusin',s.resume);
} else {
s.events.remove(window,'blur',s.freeze);
s.events.remove(window,'focus',s.resume);
}
}
};

this.show = function() {
for (var i=this.flakes.length; i-- {
this.flakes[i].o.style.display = 'block';
}
};

this.SnowFlake = function(parent,type,x,y) {
var s = this, storm = parent;
this.type = type;
this.x = x||parseInt(rnd(screenX-20),10);
this.y = (!isNaN(y)?y:-rnd(screenY)-12);
this.vX = null;
this.vY = null;
this.vAmpTypes = [1,1.2,1.4,1.6,1.8]; // "amplification" for vX/vY (based on flake size/type)
this.vAmp = this.vAmpTypes[this.type];
this.melting = false;
this.meltFrameCount = storm.meltFrameCount;
this.meltFrames = storm.meltFrames;
this.meltFrame = 0;
this.twinkleFrame = 0;
this.active = 1;
this.fontSize = (10+(this.type/5)*10);
this.o = document.createElement('div');
this.o.innerHTML = storm.snowCharacter;
this.o.style.color = storm.snowColor;
this.o.style.position = (fixedForEverything?'fixed':'absolute');
this.o.style.width = storm.flakeWidth+'px';
this.o.style.height = storm.flakeHeight+'px';
this.o.style.fontFamily = 'arial,verdana';
this.o.style.overflow = 'hidden';
this.o.style.fontWeight = 'normal';
this.o.style.zIndex = storm.zIndex;
docFrag.appendChild(this.o);

this.refresh = function() {
if (isNaN(s.x) || isNaN(s.y)) {
// safety check
return false;
}
s.o.style.left = s.x+'px';
s.o.style.top = s.y+'px';
};

this.stick = function() {
if (noFixed || (storm.targetElement !== document.documentElement && storm.targetElement !== document.body)) {
s.o.style.top = (screenY+scrollY-storm.flakeHeight)+'px';
} else if (storm.flakeBottom) {
s.o.style.top = storm.flakeBottom+'px';
} else {
s.o.style.display = 'none';
s.o.style.top = 'auto';
s.o.style.bottom = '0px';
s.o.style.position = 'fixed';
s.o.style.display = 'block';
}
};

this.vCheck = function() {
if (s.vX>=0 && s.vX<0.2) {
s.vX = 0.2;
} else if (s.vX<0 && s.vX>-0.2) {
s.vX = -0.2;
}
if (s.vY>=0 && s.vY<0.2) {
s.vY = 0.2;
}
};

this.move = function() {
var vX = s.vX*windOffset, yDiff;
s.x += vX;
s.y += (s.vY*s.vAmp);
if (s.x >= screenX || screenX-s.x < storm.flakeWidth) { // X-axis scroll check
s.x = 0;
} else if (vX < 0 && s.x-storm.flakeLeftOffset < 0-storm.flakeWidth) {
s.x = screenX-storm.flakeWidth-1; // flakeWidth;
}
s.refresh();
yDiff = screenY+scrollY-s.y;
if (yDiff<storm.flakeHeight) {
s.active = 0;
if (storm.snowStick) {
s.stick();
} else {
s.recycle();
}
} else {
if (storm.useMeltEffect && s.active && s.type < 3 && !s.melting && Math.random()>0.998) {
// ~1/1000 chance of melting mid-air, with each frame
s.melting = true;
s.melt();
// only incrementally melt one frame
// s.melting = false;
}
if (storm.useTwinkleEffect) {
if (!s.twinkleFrame) {
if (Math.random()>0.9) {
s.twinkleFrame = parseInt(Math.random()*20,10);
}
} else {
s.twinkleFrame--;
s.o.style.visibility = (s.twinkleFrame && s.twinkleFrame%2===0?'hidden':'visible');
}
}
}
};

this.animate = function() {
// main animation loop
// move, check status, die etc.
s.move();
};

this.setVelocities = function() {
s.vX = vRndX+rnd(storm.vMaxX*0.12,0.1);
s.vY = vRndY+rnd(storm.vMaxY*0.12,0.1);
};

this.setOpacity = function(o,opacity) {
if (!opacitySupported) {
return false;
}
o.style.opacity = opacity;
};

this.melt = function() {
if (!storm.useMeltEffect || !s.melting) {
s.recycle();
} else {
if (s.meltFrame < s.meltFrameCount) {
s.meltFrame++;
s.setOpacity(s.o,s.meltFrames[s.meltFrame]);
s.o.style.fontSize = s.fontSize-(s.fontSize*(s.meltFrame/s.meltFrameCount))+'px';
s.o.style.lineHeight = storm.flakeHeight+2+(storm.flakeHeight*0.75*(s.meltFrame/s.meltFrameCount))+'px';
} else {
s.recycle();
}
}
};

this.recycle = function() {
s.o.style.display = 'none';
s.o.style.position = (fixedForEverything?'fixed':'absolute');
s.o.style.bottom = 'auto';
s.setVelocities();
s.vCheck();
s.meltFrame = 0;
s.melting = false;
s.setOpacity(s.o,1);
s.o.style.padding = '0px';
s.o.style.margin = '0px';
s.o.style.fontSize = s.fontSize+'px';
s.o.style.lineHeight = (storm.flakeHeight+2)+'px';
s.o.style.textAlign = 'center';
s.o.style.verticalAlign = 'baseline';
s.x = parseInt(rnd(screenX-storm.flakeWidth-20),10);
s.y = parseInt(rnd(screenY)*-1,10)-storm.flakeHeight;
s.refresh();
s.o.style.display = 'block';
s.active = 1;
};

this.recycle(); // set up x/y coords etc.
this.refresh();

};

this.snow = function() {
var active = 0, used = 0, waiting = 0, flake = null, i;
for (i=s.flakes.length; i-- {
if (s.flakes[i].active === 1) {
s.flakes[i].move();
active++;
} else if (s.flakes[i].active === 0) {
used++;
} else {
waiting++;
}
if (s.flakes[i].melting) {
s.flakes[i].melt();
}
}
if (active<s.flakesMaxActive) {
flake = s.flakes[parseInt(rnd(s.flakes.length),10)];
if (flake.active === 0) {
flake.melting = true;
}
}
};

this.mouseMove = function(e) {
if (!s.followMouse) {
return true;
}
var x = parseInt(e.clientX,10);
if (x<screenX2) {
windOffset = -windMultiplier+(x/screenX2*windMultiplier);
} else {
x -= screenX2;
windOffset = (x/screenX2)*windMultiplier;
}
};

this.createSnow = function(limit,allowInactive) {
for (var i=0; i<limit; i++) {
s.flakes[s.flakes.length] = new s.SnowFlake(s,parseInt(rnd(flakeTypes),10));
if (allowInactive || i>s.flakesMaxActive) {
s.flakes[s.flakes.length-1].active = -1;
}
}
storm.targetElement.appendChild(docFrag);
};

this.timerInit = function() {
s.timers = (!isWin98?[setInterval(s.snow,s.animationInterval)]:[setInterval(s.snow,s.animationInterval*3),setInterval(s.snow,s.animationInterval)]);
};

this.init = function() {
for (var i=0; i<s.meltFrameCount; i++) {
s.meltFrames.push(1-(i/s.meltFrameCount));
}
s.randomizeWind();
s.createSnow(s.flakesMax); // create initial batch
s.events.add(window,'resize',s.resizeHandler);
s.events.add(window,'scroll',s.scrollHandler);
if (s.freezeOnBlur) {
if (isIE) {
s.events.add(document,'focusout',s.freeze);
s.events.add(document,'focusin',s.resume);
} else {
s.events.add(window,'blur',s.freeze);
s.events.add(window,'focus',s.resume);
}
}
s.resizeHandler();
s.scrollHandler();
if (s.followMouse) {
s.events.add(isIE?document:window,'mousemove',s.mouseMove);
}
s.animationInterval = Math.max(20,s.animationInterval);
s.timerInit();
};

this.start = function(bFromOnLoad) {
if (!didInit) {
didInit = true;
} else if (bFromOnLoad) {
// already loaded and running
return true;
}
if (typeof s.targetElement === 'string') {
var targetID = s.targetElement;
s.targetElement = document.getElementById(targetID);
if (!s.targetElement) {
throw new Error('Snowstorm: Unable to get targetElement "'+targetID+'"');
}
}
if (!s.targetElement) {
s.targetElement = (!isIE?(document.documentElement?document.documentElement:document.body):document.body);
}
if (s.targetElement !== document.documentElement && s.targetElement !== document.body) {
s.resizeHandler = s.resizeHandlerAlt; // re-map handler to get element instead of screen dimensions
}
s.resizeHandler(); // get bounding box elements
s.usePositionFixed = (s.usePositionFixed && !noFixed); // whether or not position:fixed is supported
fixedForEverything = s.usePositionFixed;
if (screenX && screenY && !s.disabled) {
s.init();
s.active = true;
}
};

function doStart() {
if ((this.excludeMobile && !isMobile) || !this.excludeMobile) {
window.setTimeout(function() {
s.start(true);
}, 20);
}
// event cleanup
s.events.remove(window, 'load', doStart);
}

// hooks for starting the snow
s.events.add(window, 'load', doStart, false);

return this;

}(window, document));